This invention relates to a method and an apparatus for producing an insulation displacement terminal which is designed to perform a given characteristic and to the insulation displacement terminal produced by the method.
For convenience of explanation, a conventional insulation displacement terminal and a method for producing the same will be described below by referring to FIGS. 11 to 14.
FIG. 11 is an explanatory view illustrating a method for producing a conventional insulation displacement terminal. FIG. 12 is a graph illustrating a relationship between a height of conductive wires and a compressive force in the case of producing the insulation displacement terminal by the method shown in FIG. 11. FIGS. 13A through 13C are explanatory views illustrating a change of arrangement of the conductive wires in association with compression in the case where the conductive wires of the insulation sheath cable comprise twisted wires. FIG. 14 is a front elevational view of a conventional insulation displacement terminal produced by the method shown in FIG. 11.
In general, an insulation displacement terminal 1 includes an insulation displacement blade 2 provided with a slot 3, as shown in FIG. 14. When an insulation sheath electrical cable 6 is inserted into the slot 3 from a distal end (upper end in FIG. 14) of the slot, conductive wires 7 (FIGS. 13A to 13C) come into press contact with the blade 2 while an insulation sheath 8 of the cable 6 (FIG. 11) is being cut by the blade 2, thereby completing an electrical connection between the cable 6 and the terminal 1. It has been required to set a characteristic of an insulation displacement in compliance with a kind of cable 6 being connected so as to obtain a good insulation displacement connection. FIG. 11 shows a conventional method for designing the insulation displacement terminal 1 which will satisfy such a requirement.
The method of designing the insulation displacement terminal 1 will be explained below.
First, the insulation sheath 8 of the electrical cable 6 is removed over a predetermined area to expose the conductive wires 7. Secondly, as shown in FIG. 11, a pair of probes 51 and 52 clamp the conductive wires 7 from which the insulation sheath 8 is removed. A compressive load and a height of the conductive wires are measured by changing a compressive load on the wires 7 exerted by the probe 52, as shown by an arrow. Then, in the case where the conductive wires 7 are made of a plurality of twisted wires (for example, seven twisted wires) a relationship between the compressive load and the height of the conductive wires is shown by lines 61a and 61b in FIG. 12. That is, when the twisted conductive wires 7 are subject to the compressive load, an arrangement of the wires 7 is changed, as shown in FIGS. 13A to 13C. The compressive load will alter irregularly to a point P in FIG. 12 during compression of the conductive wires 7 (a decrease of the height of the wires). When the conductive wires 7 are compressed over the point 7, however, the load rises abruptly (line 61b) since the twisted conductive wires 7 are compacted into a unit and behave as a single wire.
Accordingly, it is preferable to determine an initial slot width A1 of the insulation displacement terminal, a terminal displacement amount B1 after being brought into an insulation displacement at a predetermined press contact position, a slot width after being brought into the insulation displacement, and a reaction force corresponding to the terminal displacement amount B1 so that the insulation displacement will occur in an area within a point Q in FIG. 12 on which the load rises up abruptly. That is, a beam width, a thickness and a slot length of the insulation displacement terminal 1 are designed so that a curve line 62, which illustrates a relationship between a displacement and a reaction force which are caused by an elastical deformation from the initial slot width A1, will pass through the point Q.
However, since the electrical cable 6 is inserted into the slot 3 in the U-shapted insulation displacement terminal 1 shown in FIG. 14 from an upper part of the slot upon an actual insulation displacement, the electrical cable 6 also receives a force in an inserting direction. The conductive wires 7 cause arrangements different from those in the case where the wires are merely compressed from the upper part, as shown in FIG. 11. In addition, in actual insulation displacement, the insulation sheath 8 of the electrical cable 6 is cut by the slot at the initial stage of the insulation displacement, and thus this cutting condition is greatly different from the condition of predeterminately removing the insulation sheath over a given area in the manner shown in FIG. 11.
Accordingly, it is difficult in the manner shown in FIG. 11 to make an accurate estimate of an actual characteristic of connection. Assuming that an initial slot width, a terminal displacement amount, and a slot width after connection in an actual insulation displacement terminal are A2, B2 and C2, respectively, B2 and C2 are deviated from B1 and C1 shown in FIG. 12. Consequently, the actual terminal is inclined to be put on a condition different from designed values.
This inclination becomes more significant as a size of the conductive wires becomes smaller. This is a serious problem upon reducing a diameter of the electrical cable and compacting a portion of the insulation displacement in association with producing more compact devices.